Abstract: Cooling has been used for the preservation of fresh produce such as fruit and vegetables due to its low cost and high effectiveness in maintaining the product quality. Recently, several researchers have conducted theoretical and experimental studies for obtaining the kinetics of cooling and cooling time for fruits with different geometries. Present work, therefore, aims to simulate the cooling of fruits with particular reference to banana, orange, strawberry and Tahiti lemon. The transient heat conduction equation and its analytical solution using Galerkin based integral method are presented. It has been found that the strawberry has lower dimensionless cooling time compared with time required to cool other fruits, which is due to its higher surface area/volume ratio value. In orange and lemon the temperature distribution was found to be homogeneous in the angular direction, while in banana and strawberry it was two-dimensional due to shape of the fruits.
Abstract: Water uptake studies of composite materials reinforced with vegetable fibers shows that they are highly sensitive to environmental influences such as water and temperature. The presence of moisture leads to impregnation and imperfect interfacial fiber-matrix adhesion, which generate internal stresses porosity and premature system failure. Accordingly, the aim of this work is to study theoretically water absorption in unsaturated polyester composites reinforced with caroá fiber (Neoglaziovia Variegata) at 25, 50 and 70°C by using a transient 3D mathematical model via ANSYS CFX® Software. The samples has composition 30% caroá fiber/70% unsaturated polyester resin and dimensions 6 x 20 x 20 mm3. Results of the average moisture content and moisture content distribution during the water uptake are presented and analyzed. Comparison between numerical and experimental data of the average moisture content showed good agreement. It can be concluded that the water absorption rate is faster in the vertex region of the composites, and mainly at higher temperature.
Abstract: This works presents new approach to model formation of expanded austenite (S-phase) during nitriding in plasma conditions. Diffusion saturation of the substrate (iron or austenite steel) is treated as interdiffusion of nitrogen and iron that involves stresses and plastic deformation and is based on the Darken scheme.
It is argued that S-phase growing at nitriding behaves as elasto-viscous Maxwell solid. During the process, in the nitride zone, the dynamic pressure appears, which is related to Darken drift and depends on metal viscosity. Basic equations are formulated and discussed. The formula for drift is derived. Exemplary results, i.e. concentration profiles, dynamic pressure and dilatation of the sample during the process, are presented. Concentration profiles confirm existence of characteristic plateau like zone in the surface adjacent zone.
Abstract: Shape memory alloys (SMA) are materials with metallic characteristic able to recover a geometric shape previously established under heat effect. This differentiated property, combined with the mechanical characteristic allows its use in many industrial situations. Active composites are produced with the polymeric matrix and wire of shape memory alloy, combining the elastic properties of the composite and characteristics of the phase transformation, martensite and austenite of SMA with memory alloy effect. The phase transformations that occur in the alloy are thermal processes, characterized by an increase in temperature during processing. The heat is transmitted for matrix, resulting in loss of mechanical properties of the composite. In this context, this paper aims to numerically analyze heat transfer in an epoxy resin polymer matrix incorporating Ni-Ti alloy wire with shape memory effect using ANSYS CFX software.
Abstract: Inlet and outlet pressure drop effects can contribute significantly to the total pressure drop in porous media if thin solid matrices are used. However, these effects are usually ignored and few are the studies that focus on this topic. This paper uses a numerical simulation approach to determine the importance of the inlet and outlet pressure drop effects on the total pressure drop in a staggered arrangement of square cylinders with equal sizes, dc. The Navier-Stokes equations are solved at the pore level for several matrix lengths (from dc to 34dc) and for several Reynolds numbers based on dc and maximum velocity of the velocity inlet profile (from 36 to 120). Accurate results of the velocity and pressure fields are obtained through the use of the immersed boundary method in combination with the finite differences method, 4th-order compact schemes for spatial discretization and 4th-order Runge-Kutta temporal discretization. The results presented in this paper confirm that the classical models (e.g., Hazen-Dupuit-Darcy model) are only valid when the solid matrix has a length above a certain value, called the critical length. For shorter porous media, the pressure drop does not vary linearly with the matrix length. The deviations to the model that occur at the shortest porous media are explained by the entrance and exit contributions to the total pressure drop that, in these cases, are not negligible when compared to the bulk pressure drop. For the staggered array of square cylinders and range of Reynolds numbers considered, the critical porous medium length is 16dc. A practical outcome of the present study is the quantification of the influence of the pressure tap locations on the measurements of pressure drop in porous media. When the matrix is short when compared to the particle diameter, care must be taken with the pressure taps placement: they should be located outside the porous matrix and not too close to its inlet and outlet sections. If the matrix is thick enough when compared to the particle diameter, the taps can be placed either inside or outside the matrix. Also, if the influence of the side walls on the total pressure drop is not high (i.e., the walls are at a relative large distance when compared to the particle diameter), there is no practical need to correct the measured pressure values to account for the influence of the walls. This correction should be considered for the shortest matrices though.
Abstract: The manufacture of clay bricks goes through several phases, among which are clay wetting, molding, drying and firing. The drying process has a high energy consumption and the material needs to be dried with control for avoid it to be unusable after drying. Optimization of the drying process (reduction of process time and energy expenditure) is crucial for the ceramist industry. In this sense, this work aims to make a transient thermal study of the temperature distribution in an industrial brick due to the energy supply of drying-air flowing inner it turbulent regime. The study is performed through numerical simulation using the software ANSYS® CFX. Transient results are displayed in terms of fields of the temperature and air velocity, and temperature of the brick. It was concluded that the higher the velocity of flow of hot air, the faster the heat diffuses into the brick. Independent of air velocity, there are temperature gradients on the surface of the brick
Abstract: This paper presents the results of an experimental investigation on gas flow and Klinkenberg effect in coal. An anthracite coal sample is subjected to a range of effective stress conditions in order to investigate a general trend of coal permeability reduction with an increase in effective stress. Based on the measured values of permeability at different mean gas pressures for constant effective stress conditions, intrinsic values of permeability in the range 0.2 – 1.5 mD and gas slip factors are determined using the Klinkenberg plot. Using measured gas permeability and calculated intrinsic permeability values, an assessment of the mean gas pressure required to minimize the Klinkenberg effect is conducted.
Abstract: This work aims to study heat and mass transfer in solids with parallelepiped shape with particular reference to drying process. A transient three-dimensional mathematical model based on the Fick ́s and Fourier ́s Laws was developed to predict heat and mass transport in solids considering constant physical properties and convective boundary conditions at the surface of the solid. The analytical solution of the governing equations was obtained using the method of separation of variables. The study was applied in the drying of common ceramic bricks. Predicted results of the heating and drying kinetics and the moisture and temperature distributions inside the material during the process, are compared with experimental data and good agreement was obtained. It has been found that the vertices of the solid dry and heat first. This provokes thermal and hydric stresses inside the material, which may compromise the quality of the product after drying.
Abstract: Salt damage can affect the service life of numerous building structures, both historical and contemporary, in a significant way. Therefore, various conservation methods have been developed for the consolidation and protection of porous building materials exposed to the salt attack. As any successful treatment of salt damage requires a multidisciplinary attitude, many different factors such as salt solution transport and crystallization, presence and origin of salts in masonry, and salt-induced deterioration are to be taken into account. The importance of pre-treatment investigations is discussed as well; in a combination with the knowledge of salt and moisture transport mechanisms they can give useful indications regarding treatment options.Another important cause of building pathologies in buildings is the rising damp and this phenomenon it is particularly more severe with the presence of salts in water. The treatment of rising damp in historic building walls is a very complex procedure. At Laboratory of Building Physics (LFC-FEUP) a wall base hygro-regulated ventilation system was developed. This system patented, HUMIVENT, has been submitted to laboratorial monitoring and to in situ validation and a numerical simplified model was developed to facilitate the practical application. Having in mind the practical application of scientific and technological knowledge from Building Physics to practice, this paper presents the design of the system (geometry, ventilation rate and hygrothermal device), the detailing and technical specification of its different components and information about the implementation in three types of buildings: a church, a museum and a residential building.